The present invention relates generally to paper machines and, more particularly, to apparatus for cutting and guiding the marginal lead-in strip formed in a paper web in connection with a lead-in operation.
Generally, cutting and guiding apparatus include nozzle tubes adapted to be connected to a source of compressed gas, nozzle apertures or the like formed in or on the nozzle tubes, and plates for guiding the passage of the lead-in strip.
The apparatus of the present invention is intended for use at locations in a paper machine where the introduction or "lead-in" of the web is accomplished by separating a narrow strip from the margin of the full-width web and conducting this so-called lead-in strip forwardly in the machine direction by means of jets of compressed air. The lead-in strip generally has a transverse dimension of between about 150 to 500 mm. This technique is utilized, for example, in connection with the transfer of the web from the last drying cylinder of the paper machine to the machine calendar or from the bottom roll of the calendar to the paper reeling apparatus.
When introducing or leading-in a web at the web transfer points using conventional techniques, the problem has been that when the separated marginal or lead-in strip, separated from the web in the manner described above, is first allowed to "flow" into a paper broke handling apparatus, i.e., the so-called pulper situated beneath the paper machine, whereupon the strip is then directed forwardly, e.g. into a first calendar throat or into the throat between a Pope cylinder and a tambour iron, that portion of the strip which has already travelled towards the pulper will also be lifted thereby tending to significantly slow down the lead-in operation due to the weight of this portion of the lead-in strip. Moreover, the paper web arriving at the throat of the next nip will be double folded, i.e. folded upon itself, which is extremely detrimental in that the rate at which the web is forwardly directed decreases thereby considerably increasing the difficulty encountered in inserting the lead-in strip between the subsequent rolls.
Attempts have been made in the prior art to avoid the drawbacks discussed above by constructing various mechanical conveyors to transport the marginal lead-in strip such, for example, as from a drying cylinder to the calendar. However, such arrangements are relatively expensive as compared to guiding the marginal strips by means of air jets and, moreover, do not reliably prevent the paper strip from arriving at the subsequent nip in a double-folded configuration.
Regarding the state of the art to which the present invention pertains, reference is made to Finnish Pat. No. 52478 (Great Britain Pat. No. 1,530,874) of the assignee of the instant application in which means are disclosed for facilitating the conduction of the web end in a paper machine. Such means comprise a chopper disposed at the transfer point of the marginal strip and adapted to cut the lead-in strip of the web into pieces prior to its conduction into the pulper while leaving an intact portion of the lead-in strip which has a length which is only sufficient to accomplish a further conduction using compressed air jets or the like. Thus, the lead-in strip provided by the apparatus of this Finnish patent is relatively short and light so as to be easily controlled and transferred by means of air jets and which can be transported to the next subsequent nip in an unfolded fashion so that the strip can be easily guided into the throat defined by the rolls. However, this arrangement has the drawback that it is relatively complex in construction and that the chopper has sharp saw blades which, of course, introduce safety problems in its operation.
Further regarding the state of the art to which the present invention pertains, reference is made to U.S. Pat. No. 3,355,349, in which cutting means in the form of a saw blade-like stationary member is situated at the lower margin of the lead-in strip guiding plate. As noted above, such blade-like members introduce safety risks into the operation of the paper machine and their operation is not always reliable.